In many aircraft systems a single drive source may only be available, but dual-redundancy in the generating system may be required for power integrity and reliability. Similarly, a four-generator power source may be necessary in a two-engine airplane.
In addition to the limitation of available drive sources in aircraft, there is also the problem that a single generator, unless oversized, may well be incapable of starting an engine. Where such a starting capability is desired, there is a need for a power generation system utilizing a machine arrangement which will overcome this problem. Finally, use of a plurality of conventional single generators would require additional mount-pads, drive-provisions, mechanical-interfaces, cooling-interfaces, and hydraulic-lines/heat exchangers.
Various tandem arrangements of electric machines are know. One such system, shown in U.S. Pat. No. 1,874,094 to Ford et al, discloses two AC machines with separate magnetic field systems in a single enclosure to form an electric transmission system. Several other U.S. patents, namely U.S. Pat. Nos. 907,176 to Richardson, 3,463,954 to Latta, 3,651,355 to Mason, and 3,717,780 to Hohne, Jr. et al, show multi-armature motors arranged in a single housing.
One progressive early approach to a dual machine-excitation method for alternators is disclosed in U.S. Pat. No. 653,088 to Hutin et al. In this patent, an in-line assembly of two machines on one shaft is shown, with the integrated machine incorporating multiple windings, including a "compensating" winding which neutralizes the effects of flux-distortion caused by armature reaction. The machine provides an excitation and voltage-regulation means which permits the AC generator to supply varying loads, and loads with different power factors.
The '088 invention was a precursor of more modern aircraft-type generators, where a DC exciter is mounted on the same shaft as the field of the alternator (AC generator). In these machines, the armature (AC winding) of the exciter is carried on the rotor and its AC output is rectified by diodes, also mounted on the rotor. The rectified AC output of the exciter is then applied to the field of the alternator. Regulation of the output AC voltage in these machines is effected by current-changes in the DC (stator) winding of the exciter.
The '088 and later machines, while using more than one electric machine in a single housing and mounting more than one rotor winding on a common shaft, nevertheless do not recognize, disclose or address the initial start, power generation, mounting, cooling and disconnect problems associated with aircraft and solved by the present invention. These problems have been recognized and solved herein by mounting and mechanically and electrically phase-aligning and electro-magnetically identical machines to permit separate or paralleled operation.
None of the aforementioned prior art approaches to power generation provide either a dual-redundancy of electric power in a single-powerplant, simultaneously providing integrated-cooling and a common mechanical interface with an aircraft engine drive, or a rapid and effective disconnect device for disconnecting such powerplants to prevent energy overloads.
In view of the inherent limitations and problems associated with aircraft applications and the above prior art approaches, there is a need to provide an aircraft power generation system that is utilizable and highly desirable where the number of available drive sources may be limited. Such a power generation system should ideally be capable of alleviating several problems associated with known aircraft-single generator arrangements; namely, that such single generators, unless oversized, are often incapable of starting an engine, require additional mount-pads, additional drive-provisions, additional mechanical-interfaces, additional cooling-interfaces, and additional hydraulic-lines/heat exchangers.
From the foregoing it can be seen that it is a primary object of this invention to provide a novel aircraft power generation system which includes a dual AC generator arrangement within a single housing. The generators are adapted to be driven by a single aircraft drive source to provide dual-redundancy in the aircraft power generation system for power integrity and reliability.
It is also an object of this invention to provide an aircraft "dual-generator" configuration in a single "tandem-generator" housing which utilizes one drive-power source, one mechanical-interface, and one cooling medium.
A still further object of the present invention is to provide a tandem-generator power system which improves source reliability of an aircraft electrical power system that has a high priority placed upon the loads.
Yet another object of the present invention is to provide a power generation system having a duality of power supply from a single engine driven source that can be mounted as a single entity on an aircraft engine pad, and that can have a single interface with a cooling fluid supply.
A still further object of the present invention is to provide a fast-acting mechanical shaft-disconnect control that can isolate an aircraft engine from a remote-driven accessory to protect it against mechanical-seizures and other problems.